Alkaline phosphatase is an enzyme which is typically expressed in cells of calcified tissues: osteoblasts, odontoblasts and hypertrophic chondrocytes. Its exact function is unknown; however, in bone it may play a role in mineralization. In the human genetic disease infantile hypophosphatasia, the deficiency in this enzyme is linked to lack of mineralization. Our initial attempts centered on cloning the human gene for bone alkaline phosphatase. However, eventually we isolated genomic clones comprising various parts of the corresponding rat gene. Two of these genomic clones, representing the beginning and the end of this gene are in advance stage of characterization. In addition, we initiated studies of the molecular regulation of alkaline phosphatase expression: using recombinant DNA techniques we produce genetic constants containing various parts of this gene and introduce them into rat bone cells, in order to study their function.